Production of dense soda ash via monohydrate and sesquicarbonate methods from bicarbonate containing solutions is believed to be conventional. Dense soda ash production by the monohydrate method is described in U.S. Pat. No. 6,589,497. According to U.S. Pat. No. 6,589,497, the solution including bicarbonate is purified by conventional techniques and sodium bicarbonate is converted into sodium carbonate in the stripping column (single or double stage).2 NaHCO3→Na2CO3+CO2+H2O
The rest of the bicarbonate that could not be converted within the stripping columns is converted by using caustic within the neutralization process.NaHCO3+NaOH→Na2CO3+H2O
Decarbonated solution is fed to the monohydrate crystallizer after being concentrated within evaporator. The slurry formed within the crystallizer is sent to the centrifuging process. Here, the monohydrate cake and the filtrate are separated from each other. Due to increasing concentration of the solution, the impurities within the solution also become concentrated. In order to achieve a marketable product quality, the impurities should be kept at a constant concentration. For this purpose, part of the filtrate is regularly purged. The purge rate is decided considering the amount of impurities within the solution including bicarbonate and the marketable product quality. The monohydrate cake effluent from the centrifuging process is dried in the rotary or fluidized bed driers (direct flame contact or indirect steam driers may be used) and thus dense soda ash is obtained. The purge is used to produce sodium carbonate decahydrate crystals within the decahydrate crystallization system. These crystals are melted and sent back to the monohydrate crystallization process. The filtrate effluent from the decahydrate centrifuge is the final purge from the system. The decahydrate crystals reject the impurities from their crystal structure. Due to this property, product recovery and decrease in the final waste amount is achieved. However, the bicarbonate content in the solution is completely neutralized and thus a significant amount of caustic is consumed. Yet, according to the phase diagram, instead of completely neutralizing, it is sufficient to decrease the bicarbonate content down to values just below the invariant point in order to obtain only sodium carbonate monohydrate crystals in the crystal phase. Thus the caustic consumption may be decreased.
Dense soda ash production via another similar process is described in U.S. Pat. No. 6,576,206. However, it is stated that, with solutions having bicarbonate concentration below the invariant point may be fed to the crystallizer and still monohydrate crystals may be obtained. U.S. Pat. No. 6,576,206 does not indicate any neutralization process. However, the significant amount of product loss with the purge to be discarded from the system is not taken into consideration. As explained below, it may be possible to send the purge stream to a Decahydrate Process to minimize the product loss and the final process waste. On the other hand, it may be possible to alter the operation parameters of the decahydrate process and switch to sesquicarbonate crystals production, considering the concentration of impurities in the bicarbonate containing solution and the system. Following this, the sesquicarbonate crystals may either be melted and recovered in the monohydrate process or fed to the light soda ash process and recovered as light/medium soda ash product. In this manner, it may be possible to apply two different processes within the same equipment and thus increase the product variety.
Production of sodium bicarbonate form the solutions obtained from nahcolite ore reserves by high temperature dissolution, by the carbonation process is described in U.S. Pat. No. 6,609,761 and U.S. Pat. No. 6,699,447. Through out the world, Sodium Carbonate production is believed to be carried out by decarbonation, purification, carbonation and drying process steps since 1800s.
The conventional method of sodium bicarbonate production process is applied to the solutions obtained from the nahcolite ore reserves. Application of this process to the solutions obtained by solution mining of trona, nahcolite and wegscheiderite ore reserves and to the lake waters including bicarbonate is not explained in this previous technique.
Production of decahydrate crystals from solutions containing bicarbonate obtained by solution mining is described in U.S. Pat. No. 5,283,054. Prior to decahydrate crystallization, all of the bicarbonate within the solution is neutralized by caustic soda addition. The caustic soda utilized for this purpose is produced by treating a portion of the raw solution including bicarbonate with calcium oxide. Since the decahydrate crystal rejects the impurities, the purity of the caustic soda solution to be used within this process is not essential. For this purpose, it may be beneficial to produce the caustic soda from monohydrate purge instead of the raw solution, considering the cost and waste management issues.
The glass producers in European, Middle East and North African markets are believed to mainly use dense soda ash. The textile and detergent industries of the same markets are believed to prefer light soda ash. The light soda ash is produced by the synthetic method for this market. Although both dense and light soda ash have the same chemical properties, they differ from each other considering bulk density and granular structure. The bulk density of dense soda ash is 0.90 to 1.3 gr/cm3 where as that of light soda ash is 0.45 to 0.65 gr/cm3. Light soda ash is in powder form. The particle size distribution of dense soda ash is between 0.15 mm and 1 mm.
Sodium carbonate production is performed both in synthetic and natural soda processes via conventional methods (carbonation). In these methods, the solution fed to the sodium bicarbonate production process is purified and sent to the carbonation columns. The sodium bicarbonate crystals obtained from the carbonation columns are centrifuged, dried and thus sodium bicarbonate product obtained.
The commercial dense soda ash product is regulated with respect to particle size. Generally, the rate of the particles smaller than 75 μm is desired to be less than 1% in the dense soda screen analyze. In order to produce such a product, vibratory screens are used at the drying process (150). Sodium carbonate monohydrate crystals may vary in particle size distribution due to impurities within the fed solution consisting bicarbonate (109) and the changes in operational conditions of the crystallizer (130). Generally, the rate of the particles smaller than 75 μm is about 2 to 5%. In conventional techniques, the under screen dense soda ash and the light and dense soda ash dusts held at the dedusting systems are dissolved again and fed to the monohydrate crystallizer.
Conventionally, the soda ash fines having lower economical value due to particle size are dissolved and fed back to the production process. Nevertheless, this method is wasteful considering the final product cost.
On the other hand, a process for melting the light soda ash or soda ash fines together with sodium carbonate decahydrate crystals at high temperature in order to obtain sodium carbonate monohydrate crystals and production of dense soda ash via drying of these crystal is described in U.S. Pat. No. 5,759,507.9 Na2CO3+Na2CO3.10 H2O→10 Na2CO3.H2O